Modern heating systems require thermostatic valves (or as they are often called, thermoregulators) to be installed onto the heating radiators and collectors for «warm floors» (see Figure 34). A thermoregulator includes two mandatory components — a thermostatic regulatory valve (a.k.a. valve) and a mechanism forcing the valve stock (thermostatic head or thermoelement). By definition, the thermostatic valve allows regulation of the heat supply of the heating device of the heating system, changing the supply of warmth carrier through the device depending on changes in the air temperature in the room. The valve consists of a body and a spool shaft (cone) overlapping a bypassed saddle.

Thermostatic valvesThermostatic valves
Figure 34. Thermostatic valves

You can manually or automatically adjust the temperature. By turning the valve flywheel, a stem valve is driven, changing the flow cross-section of the saddle and thus changing the temperature of the heating device (radiator or convector).  It should be borne in mind that the process of manual regulation is not effective and the protective cap of the valve is not intended for manual operation and manufacturers specifically recommend against it.

In automatic management the thermal head plays the role of partner for the thermal valve. Changes in the room temperature are sensed by a thermal bulb (bellows) which is installed inside the thermal head which is filled with a special substance. When heated, it expands and changes its state of aggregation, the bellows expands and acts on the valve stock which starts to be squeezed out of the bulb. As a result, the cone covers the flow cross-section of the saddle, reducing the supply of warmth carrier (quantity regulation). Upon cooling, these events take place in the reverse order: the filler gets squeezed, the stock retracts and the cross-section is opened.

There are two main types of thermoregulator: for one-piped and two-piped systems. Thermoregulators for two-piped heating systems are designed to work with large pressure changes because the hydraulic balancing of the system mostly happens because of high pressure losses in the valves. To provide such losses, the regulator valves of the thermoregulators have high hydraulic resistance (at least ten times more than the valves for one-piped systems have) and therefore small cross-sectional area. Moreover all thermostatic valves for two-piped systems can be divided into two groups: with preset hydraulic resistance, and without it. If valves without presetting are used, then basically all the heating devices on the vertical pipeline will have approximately the same supply of warmth carrier, but this supply must be adjusted according to the power output and, to be more precise, from the warmth loss from the room, which must be compensated. For example, if more warmth carrier goes through a radiator than necessary, then the room will be overheated and if less, then the air temperature will be too low. Therefore, preferably, valves with presettings, put the correct value of setting on the valves which then provide optimal supply and comfortable temperature in each room. Don’t forget that in the heating system where the heat output of heating devices is managed using radiator thermoregulators, in order to avoid excessive noise due to significant pressure changes on the thermostatic valves, it is advisable to install automatic relief valves on the vertical pipelines.

Thermoregulators are available in three types: with manual adjustment of warmth carrier supply through the valve, with thermostatic head which is managed by a bellows, and thermal head managed by a remote thermal sensor. All three types of thermoregulators have in their lower part a valve for thermal regulation, which can be the same in all three.  The difference is in the management element — thermal head. Manually regulated thermoregulators have a scale with six numbers on the head of the valve and by rotating the head you can adjust the temperature. Usually the «0» on the scale indicates that the thermoregulator is fully closed and shows that the warmth carrier doesn’t go through the thermoregulator. In this position, an change of radiator without having to drain the warmth carrier from the heating contour is possible. «1» or «snowflake» indicates the minimal supply of warmth carrier through the radiator. This function cuts the radiator off from the warmth but prevents its freezing. The other four digits allow the adjustment of the regulator so that the air temperature in the room can be from 14–28 degrees Celsius. Manually managed thermoregulators can be installed in any position, directing the management head vertically up or horizontally towards the room. It is better to install it horizontally because then the manual thermal head can later be replaced by a thermal head with a bellows if desired, and a thermal head with a bellows can only be installed directed towards the room. The fact of the matter is that if a thermal head with bellows is directed upwards then it will be in the warm air zone which comes from the radiator, and therefore will close the supply of the warmth carrier earlier than if it was directed into the room. Putting curtains or screens on top of radiators also affects the operation of thermal heads with bellows. In such cases, manual regulation of warmth carrier supply is used, and this, you must agree, is not very convenient, so thermal heads with remote sensors are used, which measure the air temperature in the room and send a signal to the thermal head.

However, the installation of thermoregulators on heating devices creates new conditions for the whole heating system. For example, suppose it got abruptly warm outside, and the warmth losses from the house are decreased, and so the room temperature begins to go up. In this case, all the automatic thermoregulators understand this situation clearly. They need to stop the supply of warmth carrier to the radiators and they do so. As the supply of warmth carrier through the radiators tries to get to zero, then the pressure in the supply pipeline increases dramatically. It is necessary to take measures to equalize the pressure. For this, a relief valve is installed in the system, right after the circulational pump.